<html>
<head>
<script>
  var m = new Map([[1, 'x'], [2, 'y'], [3, 'z']]);
  m.forEach(function (value, key, map) {
      alert(value);
  });
</script>
</head>
<body>
Map的回调函数参数依次为value、key和map本身：
</body>
</html>
